The exercise physiology of the racing greyhound

Abstract

Greyhounds were trained to gallop at maximal running speed on a treadmill constructed for the purpose. This speed considerably exceeded maximal aerobic speed and was termed supramaximal.

A mask was used to collect expired gases into bags during runs of 7.5 to 60 seconds and over the first 8-10 minutes of the recovery period. Respiratory parameters measured included VE, V02' VC02', R, fR', VT' ventilatory equivalent of O2 uptake and ventilatory equivalent of CO2 production. Respiration was found to be synchronised with the gallop stride, enabling both a high fR and VT. Mean VE reached 6 1.kg-1.min-1. Mean V02 reached 143ml.kg-l.min-l during the 30-45 second segment of running. Lactic acid draining into the blood stream displaced CO2 from the bicarbonate buffer system, so that R rose above 1.0. The highest value of R, 2.3 occurred in the second minute of recovery.

The alactacid debt of the greyhound was found to be higher than that of man but was repaid much more rapidly because of the greyhound's superior oxygen transport system.

The cardiovascular system was studied using electromagnetic and thermodilution flowmeters, and a heart rate telemeter. Changes in blood pressure caused changes in the relationship of the very elastic aortic root and the electromagnetic transducer cuff so that accurate calibration was not possible. Reliable values of cardiac output were obtained by thermodilution. Parameters measured included HR, cardiac output, SV and PCV taken before, during and for 1 hour after running. The minimum HR whilst sleeping was also obtained, and averaged 42 b min .-1 The HR was highest during runs of 30 seconds, 318 plus/minus18 b min -1. After running it fell sharply to below 160 in the second minute of recovery then rose to 200b.min-l 10 minutes after 30 and 45 second runs. HR was close to resting levels 1 hour after running. PCV after 30 seconds of running was 63.5 + 2.1% and had returned to resting values by 1 hour. Cardiac output during high speed runs was 914 + 209ml.kg-l.min-l while SV at 2.9 + 0.6ml. kg-l was increased 32% above resting SV.

Acid-base balance of jugular venous blood was studied. Comparisons with arterial samples taken at the same time showed a useful relationship of arterial and jugular venous blood for lactate, base excess and pH. The time taken for blood lactate to reach its peak value varied with the intensity and the duration of the run. The jugular venous blood lactate level after 45 of running peaked at 181 plus or minus l5mg.dl-l (7 minutes after seconds running) , pH fell to 7.094 plus or minus 0.27, base excess to -23.4 plus or minus 2.7 mEq.l-l and PC02 to 23 + 2 mm Hg. All values had returned to resting level 1 hour after the run.

Oxygen consumption during running, alactacid debt, lactate production and distance covered were used to calculate total energy cost and relative contributions of energy sources and energy cost.m -1. Anaerobic sources were the main contributors in the first 15 seconds but in the 15-30 second segment aerobic sources supplied 53% of the energy required and in the 30-45 second segment, 79%. The energy source contributions to30 seconds of running were aerobic 30%, alactacid debt 19% and lactic acid 51%. The energy cost.m-l at supramaximal speeds was higher than predicted by formulae derived from studies of dogs at submaximal speeds. The first 7.5 seconds of running cost almost as much as the next 22.5 seconds, indicating a high cost of acceleration. This is the first quantification of the energy cost of acceleration reported.

Compared to man, the greyhound has a very high oxygen uptake during sprinting. Man's major deficiencies as a sprinter are a low maximal heart rate, small heart relative to body size and low PCV. Sprinting impedes respiration in man but aids it in the greyhound. Calculations indicate that when man runs at supramaximal speed, it costs more per metre than predicted by formulae derived at submaximal speeds and that the energy cost of acceleration is of the same order as in the greyhound although man attains a much lower peak speed.